LOCATION OF ACTION OF BURNING-RATE CATALYSTS IN COMPOSITE PROPELLANT COMBUSTION

The site and mechanism by which iron-containing burning-rate catalysts act to enhance propellant burning rate at high pressures is a subject of current controversy. This paper describes a series of experiments designed to locate the site of catalytic action and to elucidate its mechanism of action. By measuring the strand burning rates of a variety of propellants, it was shown that catalytic effectiveness increases at higher pressures. The coprecipitation of iron-containing catalysts into ammonium perchlorate did not make the catalyst more effective than adding catalyst to binder. Chemically coating ammonium perchlorate with an organoiron catalyst does not increase catalytic effectiveness when compared to mixing the catalyst into the binder. The burning-rate ratio of catalyzed to uncatalyzed propellants does not change going from normal propellants to propellants with oxidizer encapsulated in a Viton-A shell. Thus, catalysts do not act beneath the burning surface to enhance ammonium perchlorate decomposition or to catalyze oxidizer-binder heterogeneous reactions. The effectiveness of iron-containing catalysts depends on their fluidity and on the weight percent ammonium perchlorate. Propellants oxidized by substituted ammonium perchlorates that contain at least one N—H bond are efficiently catalyzed by these catalysts, but catalysis of tetramethylammonium perchlorate oxidized propellants is slight. Thus, catalysts probably act in the gas phase to increase the reaction rate of perchloric acid and its initial decomposition products. © 1969 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.